We are using lanthanide ions as probes of calcium binding sites in proteins and enzymes. By substituting lanthanide ions for calcium, it is possible to use nmr and fluorescence techniques to measure distances between two sites in the proteins. We are planning to map the active site of thermolysin and measure distances from various protons on a competitive inhibitor to the two different types of metal binding sites in the protein. We are also investigating the expansion of bovine and human serum albumin resulting from small molecule binding using fluorescence energy transfer techniques.